Interpretive Summary: In the gas chromatographic (GC) analysis of certain types of pesticides, active sites in the inlet and column cause losses and tailing of the pesticide peak. However, in the presence of complicated food extracts, the effect is reduced because the active sites are filled up by the matrix components. Thus, to avoid quantitation inaccuracies for susceptible pesticides, calibration standards are commonly prepared in matrix blanks. However, this is a very inconvenient approach because blank matrices need to be obtained and stored, extra blanks need to be extracted which takes extra time, labor, and expense, and more "dirt" builds up in the GC system due to the injection additional extracts to serve as calibration standards. Furthermore, the current policies of the Food and Drug Administration and Environmental Protection Agency in the U.S. do not permit the use of calibration standards in matrix for regulatory enforcement actions. Thus, a new approach was devised in which "analyte protectants" were used to mask the active sites in the GC system. The new concept involves the addition of chemicals to both the extracts and standards (in solvent) to overcome the matrix effects. The efficacy of 89 different potential analyte protectants were evaluated in the GC analysis of a variety of pesticides, and gulonolactone was found to work the best for all the pesticides studied. The benefits of using analyte protectants vs. alternative procedures for overcoming matrix-induced effects in quantitation include: a) simpler procedure; b) easier integration of peaks; c) lower detection limits; d) better quantitation; e) less maintenance of the GC inlet; and e) lower cost.

Technical Abstract:
A common problem in gas chromatography (GC) applications is the analyte losses and/or tailing of chromatographic peaks due to undesired interactions with active sites in the inlet and column. Analytes that give poor peak shapes or degrade have higher detection limits, are more difficult to identify and integrate, and are more prone to interferences than stable analytes that give narrow peaks. For susceptible analytes, significant peak quality improvements are obtained when matrix components are present because they fill active sites, thus reducing analyte interactions. This widely known phenomenon is called "matrix-induced chromatographic response enhancement." Several approaches have been proposed to minimize peak distortion phenomena and compensate for matrix-induced effects, which is especially important for accurate quantitation, but each approach has serious limitations for routine multi-pesticide analysis. In this study, we demonstrate the feasibility of using "analyte protectants" to provide a more convenient and effective solution to the problem than other approaches developed thus far. The protecting agents are added to extracts and standards alike to provide the chromatographic enhancement effect even for the most susceptible analytes in clean solvents (even in a very dirty GC system). In this study, we evaluated 89 different compounds to find the most suitable ones for improving chromatographic quality of the signal. Dramatic peak enhancements were achieved using compounds containing multiple hydroxy-groups, and gulonolactone appears to be the most effective protecting agent for the most pesticides that we tested.